Spark plug socket wrench

ABSTRACT

A tool for torquing threaded spark plugs having a hollow body with internal surfaces at one end for drivingly connecting to wrenching surfaces on the spark plug and with suitable means at the other end for receiving torque. The body extends about the fragile insulating case of the spark plug in the torquing position and has an internal protuberance engaging the case at a location close to the wrenching surface for resisting skewing of the tool relative to the plug.

Elited States Patent [191 Dec. 9, 1975 SPARK PLUG SOCKET WRENCH [75] Inventor: Stewart V. Bray, Allen Park, Mich.

[73] Assignee: Ford Motor Company, Dearborn,

Mich.

[22] Filed: June 28, 1972 [2]] Appl. No.: 266,914

[52] US. Cl 81/121 R [51] Int. CI. B25B 13/06 [58] Field of Search 81/125, 121 R [56] References Cited UNITED STATES PATENTS 2,832,245 4/1958 Burrows 81/125 3,745,861 7/1973 Totsu et al 81/125 FOREIGN PATENTS OR APPLICATIONS 482,475 3/1938 United Kingdom 81/125 Primary ExaminerI-Iarold D. Whitehead Assistant ExaminerJames G. Smith Attorney, Agent, or Firm-Joseph W. Malleck; Keith L. Zerschling [57] ABSTRACT A tool for torquing threaded spark plugs having a ho]- low body with internal surfaces at one end for drivingly connecting to wrenching surfaces on the spark plug and with suitable means at the other end for receiving torque. The body extends about the fragile insulating case of the spark plug in the torquing position and has an internal protuberance engaging the case at a location close to the wrenching surface for resisting skewing of the tool relative to the plug.

4 Claims, 3 Drawing Figures U.S. Patent Dec. 9 1975 SPARK PLUG SOCKET WRENCH BACKGROUND OF THE INVENTEON High speed original installation of spark plugs during the assembly of an internal combustion engine presents at least one unique problem: the possibility for breakage of the fragile insulating portion defining an electrical terminal exterior of the engine. Such breakage has been known to occur close to the lipped portion of the insulating terminal which junctures with the wrenching portion of the spark plug. In many cases such cracks go unnoticed because they are hidden by overlapping portions of the plug or are too fine it) be observed visually.

Unwanted forces can be imparted to the insulating portion by skewing of the wrench used to torque the plugs, the wrench must inherently surround the insulating portion to gain access to the wrenching surfaces of the plug. Side loads are thereby applied at the extreme end of the terminal portion easily causing cracking because of the extreme leverage of contact. The present types of spark plug Wrenches (with or without rubber inserts useful in holding the plug to the wrench) particularly exert such forces when the hex wrenching surfaces are slightly worn allowing a tilted engagement to be encouraged during torquing.

SUMMARY OF THE lNvEl lTiUN To overcome the above problem, the invention herein contemplates the provision of a socket wrench having a radially inwardly extending protuberance (perferably in the form of a metallic ring) disposed at an axial location on the interior of the socket wrench so that the inner periphery of the ring can mate snugly with the fragile portion of the spark plug at a point relatively close to the juncture of the terminal portion and the wrenching portion. This substantially reduces the bending moment that will be experienced by the fragile portion.

A specific object of this invention is the provision of a radially inwardly extending protuberance on the interior of the tool body which projects inward of a line tangent to the wrenching surfaces of the spark plug and the outer extremity of the fragile portion.

SUMMARY OF THE DRAWINGS FIG. 1 is a central sectional'view of a typical prior art socket wrench as shown in a possible use position about a spark plug.

FIG. 2 is a central sectional view of a preferred embodiment of this invention as portrayed about a typical spark plug, and

FIG. 3 is a central sectional view of an alternative embodiment of this invention also in an operative posi tion about a spark plug.

DETAILED DESCRIPTION In high volume engine assembly systems, the allotted time for installing properly torqued spark plugs is rela tively small thereby increasing the possibility of a deviation in installation. The interchangeability of personnel to perform such high volume production sequences sometimes will also lead to deviations from conven tional procedures such as orientation of the wrench to the spark plug. Although there are a variety of socket wrenches that have been designed through the years, all of the prior art devices typically have a hollow body with one end having internal wrenching surfaces (usually hexagonal in configuration) effective to mate with complementary bearing surfaces on the spark plug and a closed end having an opening suitable for connection to a torquing tool. Such a wrench is shown in FIG. 1 in one of the more deviated positions of use which can lead to an increase in plug breakage and the associated warranty costs. In the use of such wrenches, installers may decide to take a fixed position facing the front of the vehicle as it passes along an assembly line and from this single position decide to install all spark plugs that may be on different sides of an engine block requiring the operator to awkwardly reach around and apply a skewing motion on the socket wrench. If, in addition, the hexagonal wrenching surfaces on the interior of the socket wrench are somewhat worn or the depth of such surfaces is shallow, the wrench will have looseness and ability to skew about the spark plug with the plug bearing surfaces acting as the fulcrum. As a result, the spark plug, having a fragile ceramic insulating portion, will be contacted at the extreme end at A, as shown. At this contact point the bending moment on the plug will be maximized; the fragileness of the ceramic material will crack particularly at locations close to the juncture of the insulating portion and the wrenching portion. At times these cracks will be located under the flarredmetallic lip 9 and therefore will go unnoticed, or the cracks will be of such a micro dimension that they will not be visually apparent until the spark plug fails.

To overcome this problem, the embodiment of FIG. 2 represents a preferred socket wrench having a body B with a hollow interior or stepped bore 14 provided with wrenching surfaces 10 at one end 11 of the body and another end 12 having suitable means 13 for receiving driving torque from a tool (not shown). The hollow interior 14 is dimensioned to allow the wrenching surfaces 10 to engage complementary bearing surfaces 15 on the spark plug C while the remainder of body B extends spacedly about the fragile insulating portion 16 of the spark plug, the plug having the usual threaded base 17 carrying the sparking means 18 with the fragile terminal portion 16 extending longitudinally outwardly from a juncture D with portion E of the plug (carrying the wrenching surfaces).

The stepped bore 14 has one step 20 carrying the wrenching surfaces 10 and another step 21 extending somewhat commensurate with the longitudinal extent of the spark plug fragile portion 16.

A protuberance 23 in the form of an annular metallic ring is press-fit within the step 20 of the bore in a manner to provide a substantially rigid connection with body B. The ring 23 has an inner periphery 24 dimensioned to mate and engage with the outer cylindrical surface 25 of the base portion 16a of the fragile portion 116; the engagement is substantially at the juncture D of the bearing surfaces 15 and the fragile terminal portion 16; in some cases, the ring may engage a part of the metallic flarred lip 9 integral with the bearing surfaces. Accordingly, misalignment of the interior of the socket wrench with the general longitudinal axis 26 is resisted. Since the ring 23 will receive resistance forces from the strongest portion of the fragile portion 16a, liklihood of excessive stress is reduced; the contact point of ring 23 with the fragile portion is located so that the bending moment is substantially reduced, additionally diluting the possibility of cracking.

Viewing the invention in a broader perspective, inward projection of the protuberance should be such that it is at least inward of a line 40 tangent to the bearing surfaces of the spark plug and the outermost extremity of the fragile portion. This is particularly brought out in the alternative embodiment of FIG. 2. The body has a stepped bore 33 with one step 33a again provided with hexagonal wrenching surfaces at one end 35 and another end 34 provided with suitable surfaces 36 for receiving the second part 37 by a press fit locked by welding. Part 37 is adapted to mate with a torquing tool which may fit within the internal surfaces 39.

The protuberance 32 has a rounded annular throat 42 which is spaced from the outer periphery of the spark plug but is designed to project radially inwardly of the tangent line 40 and is effective to prevent the type of contact occurring in FIG. 1 for the prior art embodiment.

As a cooperating feature, it is essential that the wrenching surfaces, both on the preferred embodiment and alternative embodiment, have sufficient longitudinal length 41 to provide a stable engagement with mating bearing surfaces of the spark plug. Without sufficient longitudinal engagement, the skewing and misalignment of the socket wrench is enhanced independently of the radial protuberance.

To evaluate the efficiency and improvement provided by the invention herein and in particular the embodiment of FIG. 2 a test fixture was fabricated so as to test various spark plugs mounted in a horizontal plane with each spark plug torqued to ft. lbs. The socket wrench under test was fitted snugly over the spark plug with a deflection sensor placed inside the wrench socket adjacent the contact point with the terminal portion; a ram would exert a side load on the wrench (a Tinius-Olsen 20,000 lb. electomatic testing machine). The ram was lowered at 0.03 inches per minute; the deflection and incremental loads were automatically recorded on a graph until a fracture of the insulator was audibly heard. Clearances between the internal diameter of the socket and the spark plug insulator were determined by marking contact portions of the spark plug with a colored grease and measuring the thickness or number of sheets of paper (used as shims at the point of contact) that were stained. The grease transferred to the paper and the degree of grease transferred through the several shims would determine the amount of contact. This test allowed determination of the side load as a measure of the sockets resistance to insulator breakage. For the embodiment of FIG. 2, and having a inch longitudinal dimension for the wrenching surfaces but with the metal ring axially spaced from the lip, there was an improvement of 128% over that of the embodiment of FIG. 1. Improvement in excess of 130% can be expected for the exact structure of FIG. 2. Using the protuberance shown in FIG. 3, there was a 83.2% improvement in the reduction of breakage over that of the prior art of FIG. 1. Considerable advantage is obtained by having the protuberance designed to contact as close as possible to the juncture between the metal bearing surfaces of the spark plug and the fragile terminal portions as this maximizes the reduction in bending moment.

I claim as my invention:

1. A hollow tool for use in the installation of spark plugs of the type having at least one bearing surface and having a fragile portion adjacent the bearing surface and about which said tool extends, said tool comprising:

a body having a plug-receiving stepped bore therein, a first step thereof having a configuration effective to mate with said bearing surface, a second step thereof spacedly surrounding said fragile portion when said first step mates with said bearing surface, and

a radially inwardly directed non-resilient protuberance on said body effective to engage said spark plug at a location substantially at the juncture between said bearing surface and said fragile portion whereby skewing forces between said bearing surface and tool may be more effectively resisted by said fragile portion.

2. A tool as in claim 1, in which said protuberance is comprised of a metallic ring frictionally received within said bore and having an inner periphery effective to substantially engage the entire circumferential periphery of said spark plug fragile portion substantially at the juncture between said bearing surface and fragile portion.

3. A socket wrench for use in torquing threaded spark plugs having a polygonal wrenching surface and a fragile insulating case extending to one side in central alignment with said wrenching surface, said socket wrench comprising:

a hollow body effective to surround said insulating case with one end in driving engagement with said wrenching surface and another end arranged to receive torque, means extending from body to engage said case at a location adjacent said wrenching surface to resist locating said body out of alignment with the alignment between said surface and case.

4. A socket wrench as in claim 3, in which said extending means is arranged to extend radially inward from said body beyond a line tangent to both said spark plug wrenching surface and the outermost end of said insulating case when said wrench is in operative position about said plug. 

1. A hollow tool for use in the installation of spark plugs of the type having at least one bearing surface and having a fragile portion adjacent the bearing surface and about which said tool extends, said tool comprising: a body having a plug-receiving stepped bore therein, a first step thereof having a configuration effective to mate with said bearing surface, a second step thereof spacedly surrounding said fragile portion when said first step mates with said bearing surface, and a radially inwardly directed non-resilient protuberance on said body effective to engage said spark plug at a location substantially at the juncture between said bearing surface and said fragile portion whereby skewing forces between said bearing surface and tool may be more effectively resisted by said fragile portion.
 2. A tool as in claim 1, in which said protuberance is comprised of a metallic ring frictionally received within said bore and having an inner periphery effective to substantially engage the entire circumferential periphery of said spark plug fragile portion substantially at the juncture between said bearing surfAce and fragile portion.
 3. A socket wrench for use in torquing threaded spark plugs having a polygonal wrenching surface and a fragile insulating case extending to one side in central alignment with said wrenching surface, said socket wrench comprising: a hollow body effective to surround said insulating case with one end in driving engagement with said wrenching surface and another end arranged to receive torque, means extending from body to engage said case at a location adjacent said wrenching surface to resist locating said body out of alignment with the alignment between said surface and case.
 4. A socket wrench as in claim 3, in which said extending means is arranged to extend radially inward from said body beyond a line tangent to both said spark plug wrenching surface and the outermost end of said insulating case when said wrench is in operative position about said plug. 